During fabrication of a semiconductor device, after formation of circuitry (e.g., active components) on an active surface (e.g., a front side), electrical connections, such as conductive pads (e.g., ball pads, pads that facilitate die-to-die interconnection, bond pads, etc.), contact plugs, conductive traces, conductive lines, etc., may form electrical connections with the circuitry located on the front side of the semiconductor device.
Conductive pads may also be formed on an opposite, or back side, of the semiconductor device for forming electrical connections between the active surface and the back side. Conductive vias, in the form of “through-substrate vias” (TSVs) or “through-wafer interconnects” (TWIs), may interconnect the circuitry on the active surface of the semiconductor device to a location on the back side of the semiconductor device (e.g., to contact pads, such as ball pads, pads that facilitate die-to-die interconnection, bond pads, redistribution traces, etc.) where electrical connections with the circuitry on the active surface may be established. TSVs are useful for assembling semiconductor devices in compact stacked, or three-dimensional (3D), arrangements.
Thus, conductive pads on the front side, the back side, or both, may be in electrical communication with circuitry on the active surface of the semiconductor device. The conductive pads may be configured to create an electrical path between circuitry on the front side of the semiconductor device and another structure, such as external circuitry including a circuit board (e.g., a printed circuit board (PCB)), an interposer, another semiconductor device (e.g., a memory device, a logic device), etc.
After formation of the conductive pads, the conductive pads may be tested to confirm proper electrical communication between the conductive pads and circuitry of the active surface. The semiconductor device may be tested with a wafer prober using a probe card that interfaces between an electronic test system and the semiconductor device (e.g., a wafer or die). Referring to FIG. 1, probe pins of the probe card may be brought into physical and electrical contact with conductive pads 110 of a semiconductor device 100. Contact of the probe pins of the probe card with conductive pads 110 may at least score or scratch the surfaces of the conductive pads 110, leaving what are referred to in the industry as “probe marks” 115. The probe marks 115 are typically formed within a center portion of each tested conductive pad 110. However, some of the probe marks 115 may fall outside of the central portion of the conductive pad 110, forming off-centered probe marks 125. Detection of off-centered probe marks 125 during post-probe inspection may cause the conductive pads 110 to not pass die inspection, even though the device is in proper working condition. One solution to the problem of off-centered probe marks has been to mask portions of the conductive pad 110 while the electrical connections of the conductive pad 110 are tested or inspected. In this manner, any off-centered probe marks 125 may be formed in the masked portions or may not be detected during inspection. However, masking portions of the conductive pad 110 requires additional processing time and adds to the overall cost of device fabrication.
During testing with the probe card, the tips of the probe pins may undesirably damage the conductive pads 110. For example, the probe tips may over-travel and penetrate through a surface of the conductive pads 110, damaging the structure of the conductive pads 110. The damaged areas are referred to in the industry as “scrub marks.” A scrub mark may provide an initiation site where corrosion of the conductive pad 110 is accelerated during subsequent device fabrication acts (e.g., during development of photoresist materials).
Referring to FIG. 2, a plan view pictomicrograph of a conductive pad 110 is shown. The conductive pad 110 includes probe marks 115 (FIG. 1) that were exposed to a developer (e.g., TMAH) that corroded the conductive pad 110 at locations of the probe marks 115, which corrosion may be particularly severe in the case of corroded scrub marks. This corrosion of the conductive pad 110 may result in a damaged portion 105 that may enhance any existing tendency toward premature device failure of the associated semiconductor device 100.
Referring to FIG. 3, a pictomicrograph of a conductive pad 110 including a damaged portion 105 formed during semiconductor testing is shown. The conductive pad 110 may be in electrical communication with a conductive plug 106. The damaged portion 105 may cause a poor mechanical (e.g., physical) and electrical connection between the conductive pad 110 and an associated conductive pillar 114 used for electrical connection to external circuitry. In some embodiments, a portion of the conductive pad 110 may remain in electrical communication with the conductive pillar 114 and the poor connection may not be detected during device testing and may undesirably comprise a portion of a completed product which, superficially, meets specifications but which will later fail in operation of the semiconductor device 100. Alternatively, the damaged portion 105 may become enlarged during subsequent processing and connections between the conductive pad 110 and surrounding materials may be damaged, leading to what is referred to in the art as “pillar fallout” in which the conductive pillar 114 becomes physically detached from the semiconductor device 100.
Referring to FIG. 4, a cross-sectional view of a semiconductor device 100 is shown. The semiconductor device 100 includes a conductive pad 110 within a dielectric material 108. The conductive pad 110 includes a damaged portion 105. The conductive pad 110 may be in electrical communication with active components on an active surface of a substrate 102 through a conductive material 104 and a conductive plug 106. The damaged portion 105 may include a crack, a void, or other discontinuity between the conductive pad 110 and at least one of the underlying conductive plug 106 and the conductive material 104. The damaged portion 105 may have been formed during probe testing of the semiconductor device 100 and may electrically isolate at least a portion of the conductive pad 110 from the underlying conductive material 104 and the conductive plug 106. During subsequent processing or during use and operation, the damaged portion 105 may become enlarged and the conductive pad 110 or materials subsequently formed on the conductive pad 110 may become detached from the semiconductor device 100, leading to premature device failure.
In addition to the aforementioned problems, surfaces of the semiconductor device 100 (e.g., the conductive pads 110) may conventionally be passivated to protect the conductive pad 110 from oxidation during subsequent processing acts. By way of example, the conductive pads 110 may be passivated with one of silicon nitride, silicon dioxide, and polyimide. Portions of the passivation may be removed with an etchant including fluorine-containing compounds to form openings through which electrical contacts to the conductive pads 110 may be formed. However, the fluorine in the fluorine-containing compounds may itself catalyze oxidation of the conductive pads 110. If the fluorinated portions of the conductive pad 110 are not removed during subsequent processing, the semiconductor device 100 may electrically or mechanically fail during production, use, or operation.
One current solution of mitigating the risks associated with damaged conductive pads 110 is to form conductive pads solely for testing the semiconductor device 100 separate from conductive pads 110 used for forming electrical connections with active circuitry of the semiconductor device 100. However, forming separate conductive test pads, as well as those for operationally connecting active circuitry, requires additional area (“real estate”) on the semiconductor device 100, undesirably increasing the cost of manufacture and the size of the semiconductor device 100. By way of example, up to about twenty-five percent (25%) of the area of the semiconductor device 100 may be used for the separate conductive test pads.